An engine can be automatically stopped to conserve fuel. A controller may judge to stop an engine based on a combination of monitored vehicle operating conditions. For example, an engine may be stopped when vehicle speed is zero and while a driver is depressing a vehicle brake actuator. Stopping the engine during such conditions may conserve fuel. However, the driver may also release the vehicle brake shortly after the engine is stopped such that little if any fuel may be conserved. Additionally, the short engine stop may be an annoyance to the driver. On the other hand, if the engine is allowed to idle for an extended amount of time before the engine is stopped, only a small amount of fuel may be conserved by stopping the engine. Consequently, it may be a challenge to realize significant fuel saving for some drivers and some driving conditions.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: automatically stopping an engine in response to one or more vehicle operating conditions meeting engine stopping criteria; and adjusting the engine stopping criteria in response to engine stopping conditions being evaluated via one or more cost functions.
By adjusting engine stopping criteria in response to weighing engine stopping conditions against one or more cost functions, it may be possible to improve vehicle fuel efficiency while limiting driver annoyance. For example, if a driver exhibits a characteristic of releasing vehicle brakes shortly after stopping a vehicle to allow the vehicle to creep, it may be desirable to increase an engine idle time after a vehicle stop to reduce the possibility of stopping the engine while the driver releases the brake. On the other hand, if the driver routinely waits several minutes before requesting vehicle acceleration after vehicle stop, it may be desirable to stop the engine just when the vehicle stops so that more fuel may be conserved.
The present description may provide several advantages. Specifically, the approach may improve vehicle fuel efficiency of an automatically stopped and started vehicle for a larger group of drivers. Additionally, the approach may reduce driver annoyance by stopping an engine when a driver expects the engine to be stopped. Further, the method may improve engine stopping and starting consistency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.